There are many types of thermally insulating glass panels. Some of them are made by coating multiple transparent and dielectric layers on glass and some are made by enclosing insulating gaps between multiple glass panels. Basically, two glass sheets separated by a vacuum space gap can greatly increase the thermally insulating effect of the glass panel.
In manufacturing glass panels having insulating gaps, three to five layers of glass are usually required to provide good insulating effect. Conventionally, getter is put into the gap between glass panels that are framed and sealed by metal. A vacuum space having air pressure below atmosphere pressure is thus formed between glass panels by the getter. Dried gas such as N.sub.2 is a suitable material for the getter because the thermal expansion coefficient of dried N.sub.2 is fairly small.
A schematic diagram of a conventional evacuated glass panel is shown in FIG. 1. To manufacture an evacuated glass panel, two flat glass sheets 101 and 102 are separated by a narrow evacuated space and hermetically sealed around the edge 103. An array of support pillars 104 maintains the separation of the two glass sheets 101 glass sheet with solder glass that is used to make the edge seal between the glass sheets 101 and 102. Evacuation takes place through the tube. The glass panel 100 thus contains a thermally insulating vacuum.
There are various evacuation methods. For example, a tube 107 may pass through a hole extending in the glass panel between the space 106 and the exterior of the glass panel. Alternatively, the tube 107 may be sealed to a hole passing from an interior face of one sheet of glass to an exterior face. FIG. 2 illustrates a sectional view of the glass panel shown in FIG. 1. As shown in FIG. 2, a small tube 107 is positioned at a corner of the glass panel 100 and sealed into one glass sheet 102 with solder glass 108. The apex of the corner is removed to accommodate the stub 105 of the tube 107. This ensures that it does not protrude beyond the nominal dimension of the glass panel 100.
The thermally insulating vacuum technique as shown in FIGS. 1 and 2 has some disadvantages. One is that customers must provide manufacturers with the specification of a glass panel in advance. In other words, users can not control by themselves the shape or size of a glass panel once the glass panel has been manufactured. Another problem is that the thermally insulating effect of such glass panels is not good enough in an environment such as a low temperature area. Even if two or three layers of such glass panels including dried N.sub.2 are used, the thermally insulating effect is still poor in the building located at low temperature areas.
One application of conventional heat insulating glass panels is in freezers. In his application, prevention of fog forming on the glass panel is the main objective and the heat insulating effect is not a significant factor in the design and production of such a glass panel. Therefore, the design and manufacture of a conventional evacuated glass panel do not satisfy the requirement of high thermally insulating effect. There is a need in improving the thermally insulating effect of an evacuated glass panel.